The study of aerodynamics is very important in the world of cycling. Wind tunnel research is conducted on most of the equipment that is used by a rider and is a critical factor in the advancement of the sport. However, to date, a comprehensive study of time-trial helmets has not been performed. This thesis presents aerodynamic data for the most commonly used time-trial helmets in professional cycling. The helmets were tested at a sweep of yaw angles, from 0⁰ to 15⁰, in increments of 5⁰. The helmets were tested at three head angle positions at each yaw angle in order to best mimic actual riding conditions. A control road helmet was used to serve as a comparative tool. In order to maintain manufacturer confidentiality, the helmets were all randomly assigned variables. Thus, the thesis presents ranges of benefit and drag numbers, but does not rank by helmet name. The testing results showed that aerodynamic helmets offer drag reduction over a standard road helmet. The best and the worst performing helmets are all more aerodynamic than a road helmet.